The present invention relates to a printing apparatus with a type-wheel, and specifically relates to the printing apparatus wherein both the original position of the type-wheel and the original position of a carriage are set by a step-out method. In this specification, above "step-out" means loss of synchronism.
In general, the printing apparatus with a type-wheel, for example, electronic typewriters are provided with at least a wheel drive motor consisting of a stepping motor for driving a type-wheel (hereinafter referred to as wheel) and a carriage drive motor consisting of a stepping motor for driving initializing setting the original position carriage, and initially setting the original position of the wheel and the original position of the carriage just after turning on power supply.
Then, the conventional printing apparatus are generally configurated in a manner that the original position of the wheel is set by the step-out method, and the original position of the carriage is set by the sensor method.
For example, as shown in the Japanese Utility Model Publication (non-examined) No. 61-112954 (FIG. 10), a sensor such as a photo interrupter outputting a carriage position detection signal is installed in the carriage, the carriage drive motor is set so as to be driven, for example, by two-phase excitation in the order of A.B phases, B.C phases, C.D phases, and D.A phases, and an operating piece operating the photo interrupter is mounted on the bottom part of a frame at nearly the center part between the left end of the frame and the position of left end (home position) of a printable range. Then, after turning on power supply, first ON or OFF of the carriage position detection signal is detected, and if it is ON, the carriage is moved rightward by 30 steps (M1 direction). Next the type-wheel is rotated clockwise (M2 direction) by two revolutions. Also, if it is OFF, the type-wheel is rotated by two revolutions in the M2 direction at that position without being moved rightward. That is , a pin installed at a place of the wheel strikes against a wheel engaging member in the carriage main unit by the first revolution, and by the second revolution, only the wheel flange attached to a motor shaft of the type-wheel drive motor is rotated while rotation of the type-wheel is restrained by the pin and the wheel engaging member, the pin energized by a spring is fitted into a notched part installed in the wheel flange, and thereby the reference position of the type-wheel is made to agree with the reference position of the type-wheel drive motor.
Then, the carriage is moved leftward step by step (M3 direction) to the position (position .circle.1 in FIG. 10) where the carriage position detection signal is ON and the excitation phases becomes predetermined phases (A.B excitation phases in this case), and that position is set as the original position of the carriage.
Next, the carriage is moved rightward by four steps (M4 direction), and at the position (position .circle.2 in FIG. 10) where the excitation phase becomes the above-mentioned predetermined phases (A.B excitation phases in this case), the carriage detection signal is confirmed to be OFF.
Furthermore, the carriage is moved leftward by 11 steps (M5 direction), and a detent is engaged with an engaging part of the wheel flange of the motor shaft by a stopper at the left end of the frame. Subsequently, the rotation of the wheel is restrained by the detent and the original position of the wheel is set by the step-out system. In this case, the wheel drive motor is rotated by one revolution in the M6 direction, and the wheel drive motor is set to the predetermined phase by a step-out operation. Then, to disengage the detent restraining the wheel, the wheel is rotated counterclockwise by 12 characters (M7 direction).
Then, the carriage is moved also to the set position of the left margin (M8 direction), and initializations of the wheel and the carriage are completed.
In addition, in the U.S. Pat. No. 4,264,220, a type-wheel original position setting apparatus is described which sets the original position of the wheel by a step-out system similar to the above-mentioned.
In the conventional electronic typewriters wherein, when power supply is turned on, the original position of the wheel is set by the step-out system, and the original position of the carriage is set by the sensor system, the original position of the carriage is set at the position .circle.1 FIG. 10, and therefore the position of mounting of the operating piece has to be set precisely so that the carriage position detection signal is ON at the position .circle.1 of predetermined excitation phase and the carriage position detection signal is OFF at the position .circle.2 of the predetermined excitation phase, that is, so that the carriage position detection signal is changed-over to ON or OFF within an allowable range of four steps equivalent to symbol L in the drawing.
In the above-mentioned case, the four-step rotation of the carriage drive motor is equivalent to a distance of about 0.8 mm of movement of the carriage. This means that the position of mounting of the operating piece has to be set within a very narrow allowable range of about 0.8 mm, and therefore mounting and positional adjustment of the operating piece are very difficult works.
For that reason, the printing apparatus has a problem that even a skilled workman necessitates much labor and time for mounting and positional adjustment of the operating piece in manufacturing and overhauling it. Then, the printing apparatus has another problem that it cannot be overhauled without a skilled workman of this kind.
Furthermore, in the case where the position of mounting of the operating piece is located close to the position .circle.1 , the operation of M2 is sometimes executed between the position .circle.1 and the position .circle.2 , and therefore the position of mounting of the stopper for operating the detent cannot be lapped over a switch mounting allowable range as shown L in FIG. 10, and is required to be set at the position a predetermined distance removed left from the allowable range, and therefore the allowable range of the position of mounting of the stopper becomes narrow, and much time is required for adjusting the position of mounting of the stopper, and accordingly this work is also a difficult work.